The founders of the Canadian League of Composers were young modernists who resented the conservative musical climate in Canada epitomized by the traditional British style of Canada's most famous composer, Healey Willan. In their first decade (1951–60), during which their membership grew from eight to more than forty and they presented dozens of concerts of new Canadian music, they struggled to find a balance between two competing goals: championing the cause of all Canadian composers, regardless of style, and promoting modern and avant-garde styles, which had been virtually ignored by the older Canadian musical establishment. This article probes how those tensions played out in two of the league's early activities: membership decisions and concert programming. Although the league did admit composers and feature works representing a wide variety of stylistic influences, its membership and concerts were nonetheless dominated by younger composers interested in modern styles, especially the group of composers in John Weinzweig's circle in Toronto. The group earned a reputation as young radicals because of their modernistic programming choices and a controversial policy that limited membership to composers younger than sixty. Although its members may not have been entirely successful in their efforts at inclusivity, the league's ground-breaking activities in the 1950s did help to establish a place for composition generally and musical modernism in particular in the postwar Canadian cultural landscape.